ADP1653
Rev. A | Page 16 of 24
In I2C mode, users select flash operation by programming the
HPLED register between 12 (01100 binary) and 31 (11111 binary).
The flash does not turn on until a strobe command is given by
either pulling the STR pin high or by writing a software strobe
command to the appropriate I2C register.
There are additional settings for the watchdog timer in I2C mode.
The strobe command operates in one of two watchdog timer
modes, timed flash and user-controlled flash, that are controlled
via the state of the timeout configuration (TMR_CFG) bit of the
CONFIG register. If TMR_CFG is set (1), the flash operates in
timed mode. In timed flash, a rising edge on STR turns on the
flash. The flash remains on until the internal timeout occurs, which
is set by the TMR_SET bits of the CONFIG register, according
to the following equation:
tFLASH = 820 ms − Code × 54.6 ms (5)
where Code ranges from 0 (0000 binary) to 15 (1111 binary),
allowing for flash periods ranging from 54 ms to 820 ms.
If TMR_CFG is not set (0), the flash operates in user-controlled
timer mode. In user-controlled timer mode, the flash remains
on as long as STR is held high. If STR remains high longer than
TFLASH (if TMR_SET = 0, tFLASH = 820 ms), the flash is turned off
and a fault is set in the watchdog timeout (FLT_TMR) bit of the
FAULT register.
The ADP1653 also offers a software strobe option, allowing the
user to turn on the flash directly through the I2C interface without
pulling the STR pin high. Setting the SW_STROBE register bit
to 1 initiates a flash cycle. The strobe can operate in either timed
or user-controlled mode, as previously described.
SAFETY FEATURES
Interrupts
For critical system conditions, such as output overvoltage,
watchdog timeout, and overtemperature conditions, the ADP1653
indicates that an interrupt event has occurred by asserting the
active-low interrupt output INT. INT is an open-drain output
and should be pulled up to the I/O voltage rail by using a resistor.
In I2C interface mode, the system baseband processor can read
the fault register through the I2C interface to determine the nature
of the fault condition after sensing that INT has gone low. Users
can clear a fault by writing 0x00 to the OUT_SEL register. This
brings INT high and clears the FAULT register.
In 2-bit logic interface mode, INT goes low for the same fault
conditions, but I2C register readback is not available. To clear
a fault, set CTRL1 and CTRL0 low.
Overvoltage Fault
The ADP1653 contains a comparator at the OUT pin that monitors
the voltage from the high power LED(s) to PGND. If the voltage
exceeds 10.15 V (typical), the ADP1653 shuts down (IQ < 45 µA)
and INT goes low. In I2C mode, Bit D0 in the FAULT register
(FLT_OV) is read back as high. The ADP1653 is disabled, and
INT remains low until the fault is cleared.
Timeout Fault
If the 2-bit logic interface is used, the maximum duration for
flash being enabled (CTRL1/CTRL0 =1) is preset to 820 ms.
If CTRL1 and CTRL0 remain high for longer than 820 ms, INT
goes low and the ADP1653 is disabled.
In I2C mode, if TMR_CFG is not set (0), and STR remains high
for longer than tFLASH (see Equation 5), INT goes low and the
FLT_TMR bit in the FAULT register is read back as high. The
ADP1653 is disabled, and INT remains low until the fault is
cleared.
Overtemperature Fault
If the junction temperature of the ADP1653 rises above 155°C,
a thermal protection circuit shuts down the LED driver and
brings INT low. In I2C mode, Bit D2 (FLT_OT) of the FAULT
register is read back as high. The ADP1653 is disabled, and INT
remains low until the fault is cleared.
Short-Circuit Fault
The HPLED pin features short-circuit protection that disables
the ADP1653 if it detects a short circuit to ground at the cathode
of the LED(s). The ADP1653 monitors the HPLED voltage once
the part is enabled in torch mode. If after 820 ms the HPLED
pin remains grounded, a short circuit is detected. INT goes low,
and Bit D3 (FLT_SCP) of the FAULT register is read back as high.
Input Undervoltage
The ADP1653 includes an input undervoltage lockout circuit.
If the battery voltage drops below the 2.7 V (typical) input UVLO
threshold, the ADP1653 shuts down and the input current drops to
less than 45 µA to prevent deep discharge of the battery. In this
case, the system register information is lost, and when power is
reapplied, a power-on reset circuit resets the registers to their
default conditions.
Current Limit
The internal LX switch limits battery current by ensuring that
the peak inductor current does not exceed 2.1 A (typical). If the
SETI, SETT, or SETF pins accidentally connect to ground,
reference current is limited to a maximum of 1 mA.